Fafnir3MM9108WITULSuper-Precision Angular Contact Ball Bearing Matched Triplex Set 40 x 68 x 15 mm, 25° Contact Angle, Light Preload, ABEC 7/9

Product Description

What this part is

A matched triplex set of super-precision angular contact ball bearings. Bore: 40 mm (1.5748 in). Outside diameter: 68 mm (2.6772 in). Width: 15 mm (0.5906 in) per bearing. Total width: 45 mm (1.7717 in) across the set. Ground faces, light preload across the set, open both faces.

Verified performance data

Contact angle: 25°.

Dynamic radial load rating C1: 20,800 N (4,670 lbf) per bearing.

Static radial load rating C0: 14,200 N (3,190 lbf) per bearing.

Limiting speed, grease: 19,700 rpm.

Limiting speed, oil: 35,800 rpm.

Precision class: ABEC 7/9, ISO P4S.

Cage type: Phenolic, outer-land-riding.

Rolling elements: Steel balls.

Bore type: Straight.

Seal type: Open.

Decoding the designation

3MM: Fafnir super-precision series, 25° contact angle. 9108: size code corresponding to the ISO 7008 envelope, 40 mm bore. WI: ground-face style for matched mounting. T: triplex, three bearings ground as one set. UL: universal light preload. The MM prefix carries P4S accuracy, ABEC 7 dimensional with ABEC 9 running accuracy.

What these specs mean in practice

A 25° contact angle carries more thrust and less speed than a 15° angle in the same envelope, which is what makes the 3MM series the choice for spindles with significant axial cutting load.

Three bearings ground as a triplex set share preload and load between them, giving higher axial and radial stiffness and higher combined capacity than a duplex pair of the same size. Light preload keeps heat generation and running torque at the low end of the preload range.

The WI ground-face style holds the ring faces flat and parallel so the set clamps up without shimming and reproduces the factory preload.

Quantity and configuration

This is a matched triplex set: three bearings ground together as one unit and supplied together as the sale unit. Total width across the set: 45 mm. The C1 and C0 ratings above are stated per bearing.

Preload and clearance

Internal clearance: preloaded, universal light preload ground into the ring faces across the set.

Mounting data

The set is mounted in the marked orientation with the face marks aligned so the ground offsets stack correctly, clamped against square ground abutment faces, and handled as a unit. Lubricant: grease or oil, suited to the phenolic cage.

Interchange guidance

Same-spec equivalents to this set: FAG B7008-E-T-P4S-TUL, SKF 7008 CD/P4ATBTA, NSK 7008A5TRSUV3TL, RHP 7008ETTULP4. A 2MM9108WI set has a 15° contact angle and a TUM or TUH set has medium or heavy preload; both share the envelope and are related sizes.